Systems and methods of implementing an electrode for cooking medium quality measurement

ABSTRACT

A fryer measures cooking medium quality, and includes a cooking vessel configured to store a cooking medium, an electrode plate completely immersed in the cooking medium, an insulator comprising a first side and a second side, wherein the first side of the insulator is fixed to the electrode plate, and a second side of the insulator is attached to a wall of the cooking vessel, a guard ring fixed to the cooking vessel and surrounding the electrode plate and insulator. The guard ring extends further away from the wall of the cooking vessel than the electrode plate. A size of a gap between the guard ring and the electrode plate is based on a height, a width, and a thickness of the electrode plate and substantially defines a gain of the electrode. A signal conditioning circuit measures the conductivity of the cooking medium applied to the electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/375,851, filed Aug. 22, 2010, the disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to systems and methods forimplementing an electrode for cooking medium quality measurement, e.g.,as in a fryer.

2. Description of Related Art

When preparing food in a fryer, the quality of the cooking medium, e.g.,the oil, may impact the quality of the food that is cooked by the fryer.As the cooking medium is used to cook food, particles of food maycontaminate the cooking medium. The flavor characteristics of each ofthese food products may become infused to a greater or a lesser degreein the cooking medium. This infusion may adversely affect food quality.Moreover, upon heating the cooking medium, the cooking medium mayundergo chemical reactions, e.g., hydrolysis, oxidation, andpolymerization. These degradations may cause products such as free fattyacids, hydroperoxides, and polymerized triglycerides. Moreover,degradation may reduce the viscosity of the cooking oils, which also maydecrease performance. In many instances, such degradation of the cookingmedium does not become apparent to the human eye until a late stage ofdegradation. Thus, there is a need to measure the quality of the cookingmedium, which directly correlates to its suitability for use in cooking.

One method of measuring the quality of cooking medium uses a senseelectrode immersed in the frying medium. The electrode is energized withan excitation voltage signal, and the resulting current flows from theenergized electrode through the cooking medium to ground. The measuredvalue of this current corresponds to the cooking medium quality, thatis, its suitability for use for cooking. Nevertheless, known electrodesystems are not suitable for use in an open fryer. First, theconstruction materials must withstand cooking oil temperatures up to 450degrees Fahrenheit (230 degrees Celsius). Second, the electrode mustresist mechanical damage from cleaning and operator equipment abuse.Thurs, the electrode must be sufficiently unaffected by contaminationfrom suspended food particles, as well as from long-term varnishing byexposure to hot cooking medium.

In addition, for use in a commercial fryer, known electrodes, inaddition to the above problems, are not small enough to mount in thecooking vessel below the cooking medium level, without interfering withthe fry baskets or other vat mechanical features. Additionally, readoutsfrom the electrodes must be sufficiently shielded such that they aresufficiently unaffected by the proximity of grounded metal objects inthe cooking vessel, e.g., the fry baskets. Thus, the electrode must besmall, but if the electrode is too small, then the electrode may not becapable of generating sufficient signal gain to generate an outputsignal of sufficient magnitude to resolve cooking medium qualitydifferences with an adequate signal to noise ratio. Cooking media mayhave very high resistance, so the electrode current is very small,requiring a large circuit gain to create a usable signal.

Known electrodes use, for example, an interdigitated pattern ofconductors deposited on a ceramic or a fiberglass substrate. Theseconductors have very small spacing. Such electrodes are too fragile foruse in a commercial fryer. Additionally, such electrodes are toosusceptible to contamination from food particles entering the smallconductor spacing. Further, known electrodes, such as those describedabove, do not comply with food safety regulations.

SUMMARY OF THE INVENTION

Therefore, a need has arisen for systems and methods for a cookingapparatus that overcome these and other shortcomings of the related art.A technical advantage of the present invention is that an electrode unitis created that complies with food safety regulations, and is durableenough for use in a commercial fryer. Moreover, the size and geometry ofthe electrode determine the magnitude of the output response. Asmentioned above, most cooking media have a very high resistance. Theelectrode current then is very small, e.g., on the order of micro-amps(μA) or nano-amps (nA). Thus, a large circuit gain is beneficial tocreate a usable signal. Nevertheless, artificially boosted circuit gainsalso amplify the system noise. This increases the need for signalfiltering and processing, and also may contribute to false readings.Thus, the invention is designed to increase output from the electrodeitself. The inherent output response from the electrode itself when acooking medium of a given quality is applied to the electrode willhereinafter be referred to as “electrode gain.” This invention usesparticular size, geometry, design, and construction of an electrode inorder to provide high electrode gain. The specific values in thisinvention have been carefully tested to provide high electrode gain asan unexpected result.

In an embodiment of the invention, an open fryer is configured tomeasure cooking medium quality within the open fryer. The open fryercomprises a cooking vessel configured to store a cooking medium, anelectrode plate completely immersed in the cooking medium, an insulatorcomprising a first side and a second side opposite the first side,wherein the first side of the insulator is fixed to a particular side ofthe electrode plate, and a second side of the insulator is attached to awall of the cooking vessel, a guard ring fixed to the cooking vessel andsurrounding the electrode plate and insulator, wherein the guard ringextends further away from the wall of the cooking vessel than theinsulator and the electrode plate, and wherein the guard ring ispositioned to form a gap between the guard ring and the electrode plate,wherein a size of the gap is based on a height, a width, and a thicknessof the electrode plate, and the gap substantially defines a gain of theelectrode, and a signal conditioning circuit that measures theconductivity of the cooking medium applied to the electrode.

In another embodiment of the invention, an open fryer is configured tomeasure cooking medium quality within the open fryer. The open fryercomprises a cooking vessel configured to store a cooking medium, anelectrode plate completely immersed in the cooking medium, an insulatorcomprising a first side and a second side opposite the first side,wherein the first side of the insulator is fixed to a particular side ofthe electrode plate, and a second side of the insulator is attached to awall of the cooking vessel, a guard ring fixed to the cooking vessel andsurrounding the electrode plate and insulator, wherein the guard ringextends further away from the wall of the cooking vessel than theinsulator and the electrode plate, and wherein the guard ring ispositioned to form a gap between the guard ring and the electrode plate,wherein a size of the gap is based on a height, a width, and a thicknessof the electrode plate, and the gap substantially defines a gain of theelectrode, and a signal conditioning circuit that measures theconductivity of the cooking medium applied to the electrode.

Other objects, features, and advantages of the present invention will beapparent to persons of ordinary skill in the art in view of theforegoing detailed description of the invention and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, needssatisfied thereby, and the objects, features, and advantages thereof,reference now is made to the following description taken in connectionwith the accompanying drawings.

FIG. 1 is a cross-sectional view of a fryer apparatus having anelectrode unit, according to an embodiment of the invention.

FIG. 2A is a side view of the electrode unit mounted to the wall of acooking vessel, without the dust cover, according to an embodiment ofthe invention.

FIG. 2B is a front view of the electrode unit shown in FIG. 2A.

FIG. 3A is an exploded view of the electrode unit, according to anembodiment of the invention; and FIG. 3B is an exploded view of theelectrode unit, according to another embodiment of the invention.

FIG. 4 is a front view of the cooking vessel, with the front wall of thecooking vessel cut out so that the electrode unit is visible, accordingto an embodiment of the invention.

FIG. 5 is a cross-sectional, enlarged view of the dotted-line box shownin FIG. 1, showing a cross-section of the electrode unit, and alsoshowing the dust cover, according to an embodiment of the invention.

FIG. 6 shows the signal conditioning circuit, according to an embodimentof the invention.

FIG. 7 shows the signal conditioning circuit, according to anotherembodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention, and their features andadvantages, may be understood by referring to FIGS. 1-7, like numeralsbeing used for corresponding parts in the various drawings.

FIG. 1 shows a cooking medium system, such as a fryer apparatus 100,according to an embodiment of the invention. Fryer apparatus 100 maycomprise at least one cooking vessel 110, e.g., a frypot, which may beconfigured to hold a cooking medium, e.g., an oil, a liquid shortening,a meltable-solid shortening, or the like, illustrated in FIG. 1 ascooking medium 115. Electrode unit 200, which will be described in moredetail with respect to FIGS. 2-4, may measure the conductivity ofcooking medium 115. Electrode unit 200 may be positioned in cookingvessel 110 and mounted to wall 125 of cooking vessel 110, such that theportions of electrode unit 200 within cooking vessel 110 may becompletely submerged in cooking medium 115. Electrode unit 200 may senda signal to a signal conditioning circuit 600, which will be describedin more detail with respect to FIG. 6. Signal conditioning circuit 600measures the signal from electrode unit, and sends a signal to acontroller (not shown) for further processing, e.g., alerting a user offryer apparatus 100 if the conductivity of cooking medium 115 dropsbelow a threshold level. The conductivity of cooking medium 115 mayindicate the quality of cooking medium 115, as described in more detailpreviously. Fryer apparatus 100 may be configured for use in a gas orelectric fryer apparatus. Although cooking vessel 110 may be suitablefor an open-well fryer, fryer apparatus 100 also may be used in apressure fryer.

FIG. 2A shows a side view of electrode unit 200, as it is mounted towall 125 of cooking vessel 110. Similarly, FIG. 2B shows a front view ofelectrode unit 200. FIG. 3 shows an exploded view of electrode unit 200,as it is mounted to wall 125 of cooking vessel 110. Electrode unit 200may comprise electrode plate 210, which may comprise stainless steel.Electrode plate 210 may be polished on one side in order to create asmooth surface. In an embodiment of the invention, electrode plate 210may be fixed to cooking vessel 110 by a flattened bolt 215, and thus,electrode plate 210 may have a hole formed at least partially throughthe center. In an embodiment of the invention, the hole may be formedall the way through electrode plate 210. Moreover, a portion of the holemay receive bolt 215, which will be described in more detail furtherherein. In an embodiment of the invention, the portion of bolt 215 thatis inserted into the hole in electrode plate 210 may be unthreaded, inorder to provide a smooth surface at electrode plate 210, as well as tocreate a tight seal to reduce or prevent cooking medium leakage.

As shown in FIG. 2B, electrode plate 210 has a width D and a height E.As shown in FIG. 2A, electrode plate 210 has a thickness F. As describedabove, a larger electrode produces a larger electrode gain, whichcorresponds to a higher quality signal generated by electrode unit 200.Nevertheless, space in cooking vessel 210 is limited by the fryingbaskets. Moreover, the electrode height E may be small enough such thatthe electrode is completely immersed in the cooking medium, even duringconditions when the amount of cooking medium is low. Although othervalues may yield similar results, an embodiment of the invention uses awidth D of electrode plate 210 of 2.000 inches (5.080 centimeters), aheight E of 0.750 inches (1.905 centimeters), and a thickness of 0.105inches (0.2667 centimeters). These values were calculated to workparticularly with the other values described in this application,particularly of the dimensions of the gap described herein. Other valuesof these dimensions may be appropriate, but these particular valuesyield the unexpected result of a relatively high electrode gain with arelatively low electrode size.

As described above, one side of electrode plate 210 may face theinterior of cooking vessel 110. The opposite side of electrode plate 210may be pressed against plate insulator 220. Plate insulator 220 may be amolded body comprising polytetraflouroethylene (“PTFE”). Plate insulator220 may comprise raised corners 225 which may assist in locating theinsulator during assembly, and which may reduce or prevent rotation ofplate insulator 220 during use. Plate insulator 220 also may include ahole formed therethrough, such that plate insulator 220 also may bethreaded through bolt 215. In an embodiment of the invention, plateinsulator 220 may comprise two separated silicone washers (not shown) inorder to provide a tighter fit, to reduce or prevent cooking mediumleakage through the hole in plate insulator 220. As shown in FIG. 2A,when installed, plate insulator 220 sits between wall 125 of cookingvessel 110, and electrode plate 210, and is aligned with electrode plate210 in the width and height directions. Plate insulator 220 has athickness C, which also may affect the electrode gain of electrode unit200. Although a thinner plate insulator 220 may increase the electrodegain, the thinner plate insulator 220 also may increase the risk thatsuspended food particles may bridge electrode plate 210 and wall 125. Inan embodiment of the invention, plate insulator 220 has a thickness C of0.0930 inches (0.2362 centimeters).

In an embodiment of the invention, plate insulator 220 also has the samewidth and height as electrode plate 210, e.g., width D and height E. Ifplate insulator 220 has a larger width or height than electrode plate210, then the electrode gain may decrease rapidly. Moreover, if plateinsulator 220 has a smaller width or height than electrode plate 210,then the electrode gain may increase, but the risk of contaminationincreases, because suspended food particles may become trapped betweenwall 125 and electrode plate 210.

Guard ring 230 may comprise a steel ring that surrounds electrode plate210 and plate insulator 220. Guard ring 230 may comprise a steel tubing,and may be formed by bending or machining a rectangular steel tubinginto a ring. In another embodiment of the invention, guard ring 230 maybe formed by welding and bending a strip of sheet stock. Guard ring 230may be fastened to wall 125 through any conventional means. In anembodiment of the invention, guard ring 220 is welded to wall 125. Inanother embodiment of the invention, guard ring 220 is integrally formedwith wall 125. Guard ring 230 may be positioned to surround electrodeplate 210, leaving a gap of distance A between each wall of electrodeplate 210 and corresponding wall of guard ring 230, as shown in FIGS. 2Aand 2B. Distance A also may affect the electrode gain of electrode unit200. A smaller gap may increase the electrode gain, but a smaller gapalso may expose the electrode unit to collecting suspended foodparticles in the gap, which may decrease the accuracy of electrode unit200. In an embodiment of the invention, distance A of the gap formed byguard ring 230 may be 0.167 inches (0.424 centimeters).

As shown in FIG. 2A, guard ring 230 has a thickness H. The thickness Hof guard ring 230 may affect the electrode gain of electrode unit 200,but by a less significant margin than the dimensions listed above.Moreover, the primary purpose of guard ring 230 may be to protect theelectrode plate 210 and insulator 220. Thus, the thickness H may beselected to provide sufficient mechanical strength to protect electrodeplate 210 and insulator 220 from damage. In an embodiment of theinvention, thickness H of guard ring 230 may be within a range of 0.075inches to 0.083 inches (0.191 centimeters to 0.211 centimeters).Similarly, guard ring 230 extends outward from wall 125 for a distanceG, as shown in FIG. 2A. Guard ring 230 may be designed to have adistance G based on the thickness of electrode plate 210 and insulator220, and also based on the desired electrode offset for increasingelectrode gain. In an embodiment of the invention, the distance G thatguard ring 230 extends from wall 125 may be 0.250 inches (0.6350centimeters). Referring again to FIG. 2A, insulator 220 and electrodeplate 210 are offset below the edge of guard ring 230 to provideadditional protection from damage and abuse. In FIG. 2A, the distance Bmay be the difference between distance G and the sum of thicknesses Cand F. Distance B may be 0.057 inches (0.145 centimeters).

Guard ring 230, insulator 220, and electrode plate 210 may be positionedon an interior side of wall 125 of cooking vessel 110, as shown in FIGS.2A and 3. In an embodiment of the invention, insulator 220, electrodeplate 210, and wall 125 have a hole in their center, such that bolt 215may pass between them, and mount electrode plate 210 and insulator 220to wall 125. Nevertheless, as shown in FIG. 2A, back insulator 225 maybe positioned next to wall 125 on an outside of wall 125, opposite theside which contacts insulator 220. Back insulator 225 may comprise PTFE,and may help reduce or prevent cooking medium from leaking through thehole in wall 125. In an embodiment of the invention, back insulator 225also may have a hole formed therethrough, through which bolt 215 maypass.

As shown in FIG. 3A, seal compression washer 240 also may be positionedbehind wall 125. Seal washer 240 may contact back insulator 225 (notshown in FIG. 3A) and compress back insulator 225 against the outsidesurface of wall 125, to create a tighter seal to reduce or preventcooking medium from leaking out of the hole in wall 125. Seal washer 240may comprise stainless steel or another suitable material. Also, asshown in FIG. 3A, seal compression washer 250 may further compress sealwasher 240, thereby tightening the seal to reduce or prevent cookingmedium from leaking out of the hole in wall 125.

As shown in FIGS. 2A and 3A, an electrode contact 260 may be positionedon the opposite side of wall 125 from electrode 220. Electrode contact260 may comprise a base plate and two terminals 265 positioned on eachside of electrode contact 260, as shown in FIGS. 2A and 3. Althoughelectrode contact 260 may comprise two terminals 265, only one terminal265 is connected to a signal conditioning circuit, such as signalconditioning circuit 600 or 700, described in more detail herein. Theother terminal 265 may balance electrode contact 260, but is notnecessarily connected to the signal conditioning circuit. Either of thetwo terminals 265 may be used to connect electrode contact 260 to thesignal conditioning circuit. Electrode contact 260 may be electricallyconnected to electrode plate 210.

As shown in FIGS. 2A and 3A, a nut 270 may be placed on an outside endof bolt 215, to secure electrode contact 260, seal compression washer250, and seal washer 240 on an outside of wall 125, and plate insulator220 and electrode plate 210 on an inside of wall 125. Nut 270 maycomprise stainless steel or other suitable material, and ensures thatthere is a conduction path between electrode contact 260 and electrodeplate 210. Moreover, as shown in FIG. 2A, electrode unit 200 alsocomprises a ground stud 205, which grounds electrode plate 210. A groundconnection (not shown) grounds electrode plate 210 to ground stud 205,which is secured, e.g., welded, to cooking vessel 110.

As noted above, FIG. 3B is an exploded view of an electrode unit 300,according to another embodiment of the invention. In FIGS. 3A and 3Blike numbers are used to described similar parts. As shown in FIG. 3B, afirst seal washer 322 and a second seal washer 332 also may bepositioned behind wall 125. First seal washer 322 may contact onesurface of an insulating washer 318 and compress insulating washer 318against the outside surface of wall 125, to create a tighter seal toreduce or prevent cooking medium from leaking out of the hole in wall125. First seal washer 322 may comprise silicon or another suitablematerial, and second seal washer 332 may comprise PTFE or anothersuitable material. In addition, as shown in FIG. 3B, a seal compressionsleeve 350 may further compress first seal washer 322 and second sealwasher 332, thereby tightening the seal to reduce or prevent cookingmedium from leaking out of the hole in wall 125.

As shown in FIG. 3B, electrode contact 260 may be positioned on theopposite side of wall 125 from an electrode (not shown). Electrodecontact 260 may comprise a base plate and two terminals positioned oneach side of electrode contact 260, as shown in FIG. 3B. Althoughelectrode contact 260 may comprise two terminals, only one terminal isconnected to a signal conditioning circuit, such as signal conditioningcircuit 600 or 700, described in more detail herein. The other terminalmay balance electrode contact 260, but is not necessarily connected tothe signal conditioning circuit. Either of the two terminals may be usedto connect electrode contact 260 to the signal conditioning circuit.Electrode contact 260 may be electrically connected to an electrodeplate (not shown).

As shown in FIG. 3B, a nut 326 may be placed on an outside end of bolt215, to secure electrode contact 260, seal compression sleeve 350, andfirst seal washer 322 and second seal washer 332 on an outside of wall125, and the plate insulator and the electrode plate on an inside ofwall 125. Nut 326 may comprise stainless steel or other suitablematerial, and ensures that there is a conduction path between electrodecontact 260 and the electrode plate. Moreover, an electrode unit (notshown) also comprises a ground stud, which grounds the electrode plate.A ground connection (not shown) grounds the electrode plate to theground stud, which is secured, e.g., welded, to cooking vessel 110.

FIG. 4 shows fryer apparatus 100 from a front view. The front walls offryer apparatus 100 have been cut away to illustrate electrode 210,guard ring 230, bolt 215, and ground stud 205. These cut-away frontwalls are represented by dotted lines in FIG. 4. FIG. 4 also shows thepositional relationship between electrode unit 200 and other parts ofthe fryer apparatus 100, e.g., cooking medium outlet 420, cooking mediuminlet 430, and sensor mechanism 450.

FIG. 5 shows an enlarged view of box X of FIG. 1. Particularly, FIG. 5shows electrode unit 200, surrounded by dust cover 290. As shown inFIGS. 3A, 3B, and 5, dust cover 290, dust cover spacer 280, and dustcover nut 295, may be included in fryer apparatus 100, and will bediscussed in more detail herein. In another embodiment of the invention,dust cover 290, dust cover spacer 280, and dust cover nut 295 may beomitted.

As shown in FIGS. 3A, 3B, and 5, dust cover 290 may be held in place bydust cover spacer 280, which may be screwed onto the end of bolt 215.Although FIG. 5 does not show nut 270, in an embodiment of theinvention, nut 270 remains on bolt 215 to maintain a tight seal of thehole through wall 215, and to ensure electrical conductivity betweenelectrode plate 210 and electrode contact 260. Dust cover spacer 280 maycomprise a wide portion at one end, which may surround bolt 215, and anarrow portion at the other end, which may be threaded. Dust coverspacer 280 may provide electrically insulated spacing to the dust cover290 away from electrode contact 260, such that electrode gain may not beaffected by dust cover 290. In an embodiment of the invention, dustcover spacer 280 may comprise a durable material with a very lowelectrical conductivity, e.g., PTFE. As shown in FIG. 5, a centralportion of dust cover 290 may be threaded through the other end of dustcover spacer 280. Dust cover nut 295 then may be threaded onto the otherend of dust cover spacer 280, such that dust cover 290 is secured. Dustcover 290 may comprise a silicone rubber.

In an embodiment of the invention, dust cover 290 may contain a slit(not shown), which may be configured to allow entry of a wire to reachelectrode contact terminal 265, which is not pictured in thisillustration. Electrode contact 260 and electrode contact terminal 265may be modified in order to accommodate dust cover 290 and slit 265. Inan embodiment of the invention, dust cover 290 prevents accumulation offoreign material, e.g., breading dust and cooking medium film, aroundthe electrode contact area.

FIG. 6 shows a high-level diagram of signal conditioning circuit 600.The complete details of this circuit are omitted, but the encloseddescription is sufficient for one of ordinary skill in the art toconstruct this circuit. The signal conditioning circuit 600 may bepowered by a ±5V DC power supply. Within the signal conditioningcircuit, oscillator 640 may create the electrode excitation signal,which in an embodiment of the invention, may be a ±2.5V square wave,with a frequency of approximately 10 Hz. The duty cycle for this squarewave may be approximately 50%. The excitation signal may be applied tothe electrode from oscillator 640 through resistor 630. Thus, thecurrent that flows through the cooking medium in the cooking vessel 110may develop a voltage potential across resistor 630 having a value R.The voltage across resistor 630 may be amplified by instrumentationamplifier 620. Then, the voltage from instrumentation amplifier 620 maybe rectified by precision full-wave rectifier 650. The rectifier outputthen may be applied to low-pass filter 660, and finally may pass throughgain stage amplifier 670. The output of gain stage amplifier 670 may bea voltage proportional to the DC current flow through the cookingmedium. In an embodiment of the invention, the value R may be 499kilo-ohms (KΩ). Nevertheless, this resistor value is based on thevarious dimensions described above for electrode unit 200, and otherembodiments may have other values.

FIG. 7 shows a high-level diagram of signal conditioning circuit 700. InFIGS. 6 and 7 like numbers are used to described similar parts. Thecomplete details of this circuit are omitted, but the encloseddescription is sufficient for one of ordinary skill in the art toconstruct this circuit. The signal conditioning circuit 700 may bepowered by a ±5V DC power supply. Within the signal conditioningcircuit, a DC voltage reference 740 may create the electrode excitationsignal, which in an embodiment of the invention, may be 3V DC. Theexcitation may be applied to the electrode from DC voltage reference 740through a resistor 730. Thus, the current that flows through the cookingmedium in cooking vessel 110 may develop a voltage potential acrossresistor 730 having a value R. Voltage across resistor 730 may bebuffered by voltage buffers 750 and 751. The buffered voltage may beamplified by instrumentation amplifier 620. The instrumentationamplifier output may then be applied to low-pass filter 660, and finallypass through gain stage amplifier 670. The output of gain stageamplifier 670 may be a voltage proportional to the DC current flowthrough the cooking medium. In an embodiment of the invention, the valueR may be about 499 kilo-ohms (KΩ). Nevertheless, this resistor value isbased on the various dimensions described above for electrode unit 200,and other embodiments may have different and appropriate values.

While the invention has been described in connection with preferredembodiments, it will be understood by those of ordinary skill in the artthat other variations and modifications of the preferred embodimentsdescribed above may be made without departing from the scope of theinvention. Other embodiments will be apparent to those of ordinary skillin the art from a consideration of the specification or practice of theinvention disclosed herein. The specification and the described examplesare considered as exemplary only, with the true scope and spirit of theinvention indicated by the following claims.

What is claimed is:
 1. An electrode unit for use in a fryer system, theelectrode unit comprising: an electrode plate comprising a first sideand a second side opposite the first side, the electrode plateconfigured to be completely immersed in cooking medium, the electrodeplate having a height, a width, and a thickness; an insulator formed onthe first side of the electrode plate and covering a surface of theelectrode defined by the height and the width; a guard ring surroundingthe electrode plate, wherein the guard ring is positioned to form a gapbetween the guard ring and the electrode plate in the height and thewidth directions, wherein a size of the gap is defined at least by theheight, width, and thickness of the electrode plate, and the gapsubstantially defines a gain of the electrode; and the second side ofthe electrode plate is a smooth polished surface.
 2. The electrode unitof claim 1, further comprising: a signal conditioning circuit configuredto receive a signal from the electrode plate, and to measure theconductivity of the cooking medium in which the electrode is completelyimmersed based on the received signal.
 3. The electrode unit of claim 1,wherein the height of the electrode is 1.905 cm, and the width of theelectrode is 5.08 cm.
 4. The electrode unit of claim 3, wherein the gapis 0.424 cm from each side of the electrode plate to its correspondingside of the guard ring.
 5. The electrode unit of claim 4, wherein theinsulator thickness is 0.2362 cm and the electrode plate thickness is0.2667 cm.
 6. The electrode unit of claim 5, wherein the guard ringextends 0.145 cm beyond the electrode plate.
 7. The electrode unit ofclaim 6, wherein the guard ring has a thickness of 0.2667 cm.
 8. Theelectrode unit of claim 1, wherein the guard ring comprises anelectrically conductive stainless steel.
 9. The electrode unit of claim8, wherein the insulator comprises PTFE.
 10. A fryer configured tomeasure cooking medium quality within the fryer, the fryer comprising: acooking vessel configured to store a cooking medium; an electrode platecompletely immersed in the cooking medium; an insulator comprising afirst side and a second side opposite the first side, wherein the firstside of the insulator is fixed to a particular side of the electrodeplate, and a second side of the insulator is attached to a wall of thecooking vessel; a guard ring fixed to the cooking vessel and surroundingthe electrode plate and insulator, wherein the guard ring extendsfurther away from the wall of the cooking vessel than the insulator andthe electrode plate, and wherein the guard ring is positioned to form agap between the guard ring and the electrode plate, wherein a size ofthe gap is defined at least by a height, a width, and a thickness of theelectrode plate, and the gap substantially defines a gain of theelectrode; and a signal conditioning circuit that measures theconductivity of the cooking medium applied to the electrode.
 11. Thefryer of claim 10, wherein the electrode plate comprises a further sideopposite the particular side, and the further side of the electrodeplate is a polished smooth surface.
 12. The fryer of claim 10, furthercomprising: a seal washer positioned on an opposite side of the wall ofthe cooking vessel from the insulator and configured to prevent cookingmedium from escaping the cooking vessel at the electrode plate; a sealcompression washer positioned on the opposite side of the wall of thecooking vessel and configured to compress the seal washer against theopposite side of the wall of the cooking vessel; and a back insulatorpositioned on the opposite side of the wall of the cooking vessel,wherein the back insulator covers the seal compression washer and isaligned with the insulator.
 13. The fryer of claim 12, furthercomprising a bolt threaded through the electrode plate, the insulator,the wall of the cooking vessel, the seal washer, the seal compressionwasher, and the back insulator.
 14. The fryer of claim 13, furthercomprising: a dust cover spacer comprising a first end and a second endopposite the first end, wherein the first end is threaded through an endof the bolt outside the cooking vessel, and the second end of the dustcover spacer is threaded; a dust cover positioned on the opposite sideof the wall that covers the seal washer, seal compression washer, andback insulator, wherein a center of the dust cover is threaded throughthe second end of the dust cover spacer; and a dust cover nut threadedthrough the second end of the dust cover spacer, and that fixes the dustcover to the dust cover spacer.
 15. The fryer of claim 10, wherein theguard ring is integrally formed with the cooking vessel.
 16. The fryerof claim 10, wherein the guard ring comprises a steel rectangulartubing.
 17. The fryer of claim 10, wherein the guard ring comprises afabricated steel stock.